Tissue ablation can be performed to remove undesired tissue such as cancer cells or may also involve the modification of the tissue without removal, such as to stop electrical propagation through the tissue in patients with a cardiac arrhythmia. Often the ablation is performed by passing energy, such as electrical energy, through one or more electrodes causing the tissue in contact with the electrodes to be heat ablated. Other devices have employed cryoprobes/catheters to freeze the tissue, other probes/catheters employing the use of such energy sources as microwaves and lasers, and high intensity ultrasonic devices mechanically causing a physical abrasion or destruction of the tissue.
The use of heat energy and cryogenic energy in combination has limited practice to date due to several factors including, but not limited to, the relatively new mainstream acceptance and utilization of ablation as a treatment option, as well as the inefficacy in utilizing each source of energy independently. Typically, two distinct thermal probes, one to deliver heat energy and one to deliver cryogenic energy are utilized, each technology having a distinct surgical skill set and approach.
Heat energy is routinely used for treating a myriad of diseases. One mode of heat treatment is radio frequency ablation (RFA). Radio frequency ablation has been used to treat a variety of cancers and cardiac anomalies. For instance, RFA has been effective in treating colorectal liver metastases. This procedure has also been used to treat saphenous vein varicoses. Other studies have shown that RFA can serve as a minimally invasive method for treating liver tumors even though it is recognized that the procedure is difficult to monitor in vivo and the blood vessels serve as a heat sink that makes it difficult to control the target temperature. Another problem using RFA in treating renal tumors is the necessity of repeat ablation to make the process more effective. Radiofrequency ablation has also been used to treat Barrett's esophagus and atrial fibrillation. When used to treat atrial fibrillation, RFA creates a risk of injury to the adjacent tissues such as the esophagus. Therefore, esophageal endoscopy is used to screen patients at risk of esophageal thermal injury after RFA.
Microwave energy has been employed with ablation catheters to try to provide sufficiently deep lesions. Since the penetration of microwaves into tissue has a steep exponential decline, the catheter is brought into close contact with the tissue. Fat, however, continues to be a significant barrier.
High powered lasers have also been applied as an ablative energy source, though have a risk of crater formation at the application. Low energy lasers produce lesions with a depth related to duration of application.
High intensity focal ultrasound (HIFU) has also been utilized since it is capable of penetrating fat and inducing fast lesions at specific depths when focused. Tissue is emulsified with millisecond boiling produced by shock wave heating. This procedure has been used to treat such disease states as cardiac arrhythmias and tumors, among others. The heated zone, however, has intact cells remaining after treatment. The treatment using HIFU also has higher complication rates than RFA when treating atrial fibrillation, halting its use in many countries.
Contrary to heat ablation, cryoablation has been utilized to freeze a target tissue. The cryogenic energy is used for treating similar diseases as targeted with heat energy. Cryoablation is used to treat a host of disease states including, but not limited to, liver tumors, actinic keratoses, breast cancer, colorectal cancer, cervical intraepithelial neoplasia, prostate cancer and atrial fibrillation. The cryogenic energy (i.e. severe cold) has the advantages of avoiding clot formation and being a natural analgesic. Although cryoablation has proven to be a successful ablation therapy, complications with the procedure exist and issues with disease recurrence remain. For example, while trying to reach a designated temperature within a target tissue, the application of freezing temperatures is extended causing overfreeze in surrounding non-targeted tissue. In an argon based system, that means a large portion of the damaged tissue is outside the targeted region. In a liquid nitrogen based system, colder isotherms are achieved throughout the iceball to increase cell death and control destruction of the targeted tissue, but overfreeze may also damage surrounding non-targeted tissue.
Given that both RFA and cryoablation are commonly used for similar procedures, the two modalities have each been evaluated for their respective advantages and disadvantages. For instance, cryoablation creates an iceball that can be easily visualized and has a defined zone; whereas RFA is difficult to visualize and can create variable temperatures especially when adjacent to a heat sink such as blood vessels. Both procedures, however, can result in survival of residual cells that may result in disease recurrence at a later point in time.
Currently, two separate, independently operated medical devices each deliver a single therapy, each having their own technical challenges and applications. Such challenges include use in a dynamic environment such as the operating room, high costs, and lengthy procedural times. Individually, present techniques are inefficient, costly, and lack a concerted effort with technologies that could have collective benefits.
A need exists for a multifunctional catheter and/or probe that utilizes the benefits of current ablative technologies but limits the undesirable effects that each individual procedure creates. The integral device will allow for heat ablation and cryoablation within a single unit for dual ablation procedures. The ablation device and method of use will be less time consuming and more effective than techniques individually utilized to date. The device will facilitate ease of use while providing cost efficient solutions to patient care.